First-order estimation method of shear wave velocity

ABSTRACT

A first-order estimation method of shear wave velocity, includes the steps of demodulating entry data, and obtaining a complex angle value, matrix average, offset matrix, displacement matrix and shear wave velocity. According to the method, the main contour of the displacement curve is extracted by the quadrature decomposition of matrix, thereby improving the signal quality of the shear wave estimation. Unlike conventional method which needs estimating twice, the shear wave displacement curve can be estimated directly to reduce estimation errors and improve estimation efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/CN2019/116431, filed on Nov. 8, 2019, which claims priority fromChinese Patent Application No. 201911051147.2 filed on Oct. 31, 2019,all of which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the technical field of ultrasonic shearwave elasticity imaging, and more particularly relates to a first-orderestimation method of shear wave velocity.

BACKGROUND

Medical ultrasound equipment evaluates tissue hardness by measuring themovement speed of shear wave in human tissue. This technology is used invarious diagnostic applications, such as evaluating liver diseases.Shear wave velocity can characterize tissue hardness characteristics toallow detection of tumors or other parts.

The conventional method of calculating shear wave velocity is:

converting an ultrasonic echo signal of a specific point into digitalecho data by an ultrasonic probe and ultrasonic equipment, in which, theultrasonic echo signal is firstly converted into an electrical signal bythe ultrasonic probe, then the electrical signal is converted intodigital echo data which can be processed by computers by the ultrasonicequipment through amplification, analog-to-digital conversion,ultrasonic beam forming and other process;

obtaining an instantaneous velocity of a particle by the echo datainformation, in which the method of obtaining instantaneous velocity issimilar to the principle of ultrasonic detection of blood flow velocity;

calculating a curve of longitudinal displacement ∫₀ ^(t)v₁(t)dt by theinstantaneous velocity v₁(t);

obtaining the displacement curve of multiple positions and calculatingthe shear wave velocity v₁(t) through the information of position andtime of the curve.

The above method needs to calculate the instantaneous velocity v₁(t) ofthe particle at first, then calculate the displacement ∫₀ ^(t)v₁(t) dt,and finally calculate the shear wave velocity v_(s)(t). The calculationprocess is complicated, and the calculated displacement curve issusceptible to the signal-to-noise ratio of the ultrasonic signal andthe human motion, resulting in inaccurate and poor stable shear wavevelocity.

SUMMARY

The present invention provides a first-order estimation method that caneasily, quickly and accurately estimate the shear wave velocity.

According to the present invention, the first-order estimation of shearwave velocity includes the following steps.

Entry data is demodulated. During an ultrasonic inspection process, anultrasonic echo signal is converted into an electrical signal by anultrasonic probe, and the electrical signal is converted into digitalecho data by an ultrasonic equipment. In this step, a data matrix isformed with different echo data obtained at different scanning positionsand different scanning times during the ultrasonic inspection process.And the data matrix is formed to an entry matrix I₁ based on IQ data incomplex form by a quadrature modulation.

Complex angle value is calculated. The complex angle value of thecomplex IQ data of each data point of the matrix I₁ demodulated by theentry data is calculated, and a real number of the corresponding datapoint is obtained to form an angle value matrix I₂.

An average evaluation of the angle value matrix is obtained. In thisstep, the real average value of all data at the same scanning positionof the angle value matrix I₂ is calculated to obtain a single-columnmean value matrix I₃.

An offset matrix is obtained. In this step, a matching matrix I₄ isintroduced. The matching matrix I₄ is a single-row matrix which has thesame columns as the angle value matrix I₂ and its data point values areall real numbers “1”. The mean matrix I₃ is multiplied by the matchingmatrix I₄ to obtain the offset matrix I₅.

A displacement matrix is obtained. In this step, by the mutualoperations of the angle value matrix I₂ and the offset matrix I₅, thedisplacement matrix I₆ is obtained. The displacement matrix I₆ is thedisplacement value of the particle that changes with time in thepropagation of the shear wave.

The shear wave velocity is calculated. In this step, the data of thedisplacement matrix I₆ is formed into multiple sets of displacementcurves on the coordinate axis, and the highest point of eachdisplacement curve is taken to calculate the shear wave velocityV_(s)(t).

In the step of entry data demodulation, the matrix rows of the datamatrix are echo information of different scanning positions; and thematrix columns are echo information at the same position at differentscanning times.

In the coordinate system where the displacement curve is located, theordinate is distance, and the abscissa is time.

The expression of the data points of the entry matrix I₁ isZ_(n)=a_(n)+b_(n)*j, and the solution formula of the data points of theangle value matrix I₂ is

A_(n) = sin⁻¹(b_(n)/a_(n)).

In the formula of the shear wave velocity,

V_(s)(t) = S_(n)/t_(n),

s_(n) is the distance difference between the highest point of eachdisplacement curve in each set of displacement curves, and t_(n) is thecorresponding time difference between the highest point of eachdisplacement curve in each set of displacement curves.

The method further includes the following steps.

The displacement curve is decomposed and reconstructed. After thesingular value decomposition of the displacement matrix I₆, aconstruction matrix I₇ is obtained based on the singular value matrixobtained by the decomposition.

Specifically, the formula for solving the reconstruction matrix I₇ isI₇=U*S*V. In this formula, U is a left singular matrix, V is a rightsingularity Matrix and S is a diagonal matrix containing singularvalues.

According to the present invention, the first-order estimation of theshear wave velocity extracts the main contour of the displacement curveby the orthogonal decomposition of matrix, thereby improving the signalquality of the shear wave estimation. And unlike conventional method,which needs estimating twice, the present invention can estimate theshear wave's displacement curve directly to reduce estimation errors andimprove estimation efficiency.

DETAILED DESCRIPTION OF THE EMBODIMENT

The invention will be described in detail with embodiments.

A first-order estimation method of shear wave velocity in an embodimentof the invention takes a complex matrix of a 4 by 9 array as the entrymatrix I₁ as an example. The specific operation process is as follows.

First is the entry data demodulation. A data matrix is formed withdifferent echo data obtained at different scanning positions anddifferent scanning times during the ultrasonic inspection process. Andthen the data matrix is formed to an entry matrix I₁ by a quadraturemodulation. The entry matrix I₁ takes IQ data in complex form as datapoints. Specifically, in demodulation, the matrix rows of the datamatrix are echo information of different scanning positions; and thematrix columns are echo information at the same position at differentscanning times. The obtained entry matrix I₁ is as follows.

$\begin{matrix}\begin{matrix}{3.5894 +} \\0.00031\end{matrix} & \begin{matrix}{3.3804 +} \\0.00021\end{matrix} & \begin{matrix}{3.3800 +} \\0.00021\end{matrix} & \begin{matrix}{3.3649 +} \\0.00021\end{matrix} & \begin{matrix}{3.3233 +} \\0.00001\end{matrix} & \begin{matrix}{3.3418 -} \\0.00021\end{matrix} & \begin{matrix}{3.3835 +} \\0.00011\end{matrix} & \begin{matrix}{3.3650 +} \\0.00031\end{matrix} & \begin{matrix}{3.3659 +} \\0.00031\end{matrix} \\\begin{matrix}{2.0188 -} \\0.00131\end{matrix} & \begin{matrix}{2.0103 +} \\0.00131\end{matrix} & \begin{matrix}{2.0196 -} \\0.00131\end{matrix} & \begin{matrix}{2.0070 +} \\0.00131\end{matrix} & \begin{matrix}{1.8600 -} \\0.00141\end{matrix} & \begin{matrix}{1.8566 -} \\0.00151\end{matrix} & \begin{matrix}{1.9991 -} \\0.00141\end{matrix} & \begin{matrix}{2.0382 -} \\0.00121\end{matrix} & \begin{matrix}{2.0344 -} \\0.00131\end{matrix} \\\begin{matrix}{0.3881 +} \\0.00081\end{matrix} & \begin{matrix}{0.4011 +} \\0.00081\end{matrix} & \begin{matrix}{0.3756 +} \\0.00081\end{matrix} & \begin{matrix}{0.4688 +} \\0.00081\end{matrix} & \begin{matrix}{0.5371 +} \\0.00081\end{matrix} & \begin{matrix}{0.4719 +} \\0.00081\end{matrix} & \begin{matrix}{0.3979 +} \\0.00081\end{matrix} & \begin{matrix}{0.3781 +} \\0.00081\end{matrix} & \begin{matrix}{0.3921 +} \\0.00081\end{matrix} \\\begin{matrix}{1.3173 +} \\0.00021\end{matrix} & \begin{matrix}{1.3200 +} \\0.00021\end{matrix} & \begin{matrix}{1.3138 +} \\0.00021\end{matrix} & \begin{matrix}{1.2204 -} \\0.0001\end{matrix} & \begin{matrix}{1.3273 +} \\0.00001\end{matrix} & \begin{matrix}{1.3273 +} \\0.00021\end{matrix} & \begin{matrix}{1.3089 +} \\0.00031\end{matrix} & \begin{matrix}{1.3004 +} \\0.00001\end{matrix} & \begin{matrix}{1.3041 +} \\0.00021\end{matrix}\end{matrix}$

Then the complex angle of the entry matrix I₁ is calculated. The complexangle value of the complex IQ data of each data point of the matrix I₁demodulated by the entry data is calculated, and the real number of thecorresponding data point is obtained to form an angle value matrix I₂.The expression of the data points of the entry matrix I₁ isZ_(n)=a_(n)+b_(n)*j, and the solution formula of the data points of theangle value matrix I₂ is

A_(n) = sin⁻¹(b_(n)/a_(n)).

The obtained angle value matrix I₂ of the 4 by 9 array in thisembodiment is as follows, and its data points are all real numbers.

$\begin{matrix}0.0786 & 0.0733 & 0.0682 & 0.0521 & 0.0068 & {- 0.0680} & 0.0319 & 0.0943 & 0.0858 \\{- 0.5822} & {- 0.5810} & {- 0.5732} & {- 0.5800} & {- 0.6550} & {- 0.6889} & {- 0.5965} & {- 0.5500} & {- 0.5562} \\1.1252 & 1.1211 & 1.1449 & 1.0734 & 0.9819 & 1.0489 & 1.1224 & 1.1451 & 1.1318 \\0.1651 & 0.1653 & 0.1863 & {- 0.0351} & 0.0042 & 0.1440 & 0.2091 & 0.1971 & 0.1781\end{matrix}$

The average of the matrix based on the angle value matrix I₂ isobtained. In this step, the real average value of all data at the samescanning position of the angle value matrix I₂ is calculated to obtain asingle-column mean value matrix I₃. The average calculation method isconventional, which is to calculate the average value of all data in thesame column. For this embodiment, for the above column contains 9 data,the formula of average value of the column is m=(i₁+i₂+ . . . i₉)/9.Specifically, the mean matrix I₃ of the 1 by 4 array in this embodimentis obtained as follows.

$\begin{matrix}0.0470 \\{- 0.5959} \\1.0994 \\0.1349\end{matrix}$

An offset matrix on the base of mean matrix I₃ is obtained. In thisstep, a matching matrix I₄ is introduced. The matching matrix I₄ is asingle-row matrix which has the same columns as the angle value matrixI₂ and its data point values are all real numbers “1”. The mean matrixI₃ is multiplied by the matching matrix I₄ to obtain the offset matrixI₅.

That is, the offset matrix I₅ is the product of the mean matrix I₃ andthe matching matrix I₄. The specific offset matrix I₅ in this embodimentis as follows.

$\begin{matrix}0.0470 & 0.0470 & 0.0470 & 0.0470 & 0.0470 & 0.0470 & 0.0470 & 0.0470 & 0.0470 \\{- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} & {- 0.5959} \\1.0994 & 1.0994 & 1.0994 & 1.0994 & 1.0094 & 1.0094 & 1.0094 & 1.0094 & 1.0094 \\0.1349 & 0.1349 & 0.1349 & 0.1349 & 0.1349 & 0.1349 & 0.1349 & 0.1349 & 0.1349\end{matrix}$

By mutual operations of the angle value matrix I₂ and the offset matrixI₅, a displacement matrix I₆ is obtained. The displacement matrix I₆ isthe displacement value of the particle that changes with time in thepropagation of the shear wave. Actual

$\begin{matrix}0.0317 & 0.0263 & 0.0212 & 0.0051 & {- 0.0402} & {- 0.1150} & {- 0.0151} & 0.0473 & 0.0386 \\0.0137 & 0.0149 & 0.0227 & 0.0159 & {- 0.0591} & {- 0.0930} & {- 0.0006} & 0.0459 & 0.0396 \\0.0258 & 0.0217 & 0.0456 & {- 0.0260} & {- 0.1175} & {- 0.0505} & 0.0230 & 0.0457 & 0.0324 \\0.0302 & 0.0304 & 0.0514 & {- 0.1700} & {- 0.1307} & 0.0091 & 0.0742 & 0.0622 & 0.0432\end{matrix}$

displacement matrix I₆ is the difference between the angle value matrixI₂ and the offset matrix I₅. That is, the corresponding data points ofthe matrix are performed operation to obtained the displacement matrixI₆. The displacement matrix I₆ of the present embodiment is as follows.

The shear wave velocity is calculated by the displacement matrix I₆. Inthis step, the data of the displacement matrix I₆ is formed intomultiple sets of displacement curves on the coordinate axis, and thehighest point of each displacement curve is taken to calculate the shearwave velocity V_(s)(t). In the coordinate system where the displacementcurve is located, the ordinate is distance, and the abscissa is time. Inthe formula of the shear wave velocity,

V_(s)(t) = s_(n)/t_(n),

s_(n) is the distance difference between the highest point of eachdisplacement curve in each set of displacement curves, t_(n) is thecorresponding time difference between the highest point of eachdisplacement curve in each set of displacement curves.

After the shear wave velocity is obtained, an orthogonal decompositionand reconstruction of the displacement curve can be performed to furtherremove the noise of the displacement curve, and keep the most criticalmessage of the displacement curve, so as to make displacement curve moreprecise and the final estimation more accurate. Specifically, itincludes the following steps.

The displacement curve is decomposed and reconstructed. After thesingular value decomposition of the displacement matrix I₆, aconstruction matrix I₇ is obtained based on the singular value matrixobtained by the decomposition.

After performing singular value decomposition on the displacement matrixI₆, a left singular matrix U, a diagonal matrix S containing thesingular values and a right singular matrix V can be obtained.

The left singular matrix U in the present embodiment is a 4 by 4 arraymatrix, as follows:

$\begin{matrix}{- 0.3039} & {- 0.6081} & 0.5690 & {- 0.4627} \\{- 0.3022} & {- 0.5204} & {- 0.0707} & 0.7955 \\{- 0.4905} & {- 0.1847} & {- 0.7645} & {- 0.3752} \\{- 0.7587} & 0.5703 & 0.2946 & 0.1110\end{matrix}$

The diagonal matrix S of the singular values in the present embodimentis a 4 by 9 matrix, as follows:

$\begin{matrix}0.2979 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0.1796 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0.0496 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0.0154 & 0 & 0 & 0 & 0 & 0\end{matrix}$

The right singular matrix Vin the present embodiment is a 9 by 9 matrix,as follows:

$\begin{matrix}{- 0.1656} & {- 0.0775} & 0.1257 & {- 0.6553} & 0.3007 & 0.5959 & 0.2290 & {- 0.1447} & {- 0.0500} \\{- 0.1551} & {- 0.0582} & 0.1264 & {- 0.3299} & {- 0.5327} & {- 0.2042} & 0.4224 & 0.3778 & 0.4485 \\{- 0.2505} & {- 0.0213} & {- 0.1843} & {- 0.2033} & 0.6883 & {- 0.5163} & {- 0.0523} & 0.1781 & 0.2946 \\0.4544 & {- 0.5764} & {- 0.5718} & 0.0766 & 0.0759 & 0.1695 & 0.2436 & 0.1474 & 0.1137 \\0.6276 & 0.0132 & 0.6589 & 0.0722 & 0.3042 & {- 0.0571} & 0.1775 & 0.1555 & 0.1234 \\0.2718 & 0.7397 & {- 0.3538} & {- 0.0516} & 0.0367 & 0.2959 & {- 0.0869} & 0.2810 & 0.2751 \\{- 0.2110} & 0.2649 & {- 0.0861} & 0.3984 & 0.1788 & {- 0.0133} & 0.8026 & {- 0.1392} & {- 0.1536} \\{- 0.3285} & {- 0.1425} & 0.1416 & 0.2832 & 0.1248 & 0.3142 & {- 0.0976} & 0.7712 & {- 0.2301} \\{- 0.2431} & {- 0.1419} & 0.1434 & 0.4097 & 0.0702 & 0.3439 & {- 0.1202} & {- 0.2561} & 0.7274\end{matrix}$

Specifically, the solution formula of the reconstruction matrix I₇ isI₇=U*S₀*V^(T), in which S₀ is the diagonal matrix based on the first twosingular values, and V^(T) is the right singular matrix based on thefirst 4 columns.

$\begin{matrix}0.2979 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0.1796 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0\end{matrix}$

The reconstruction matrix I₇ after reconstruction in the presentembodiment is as follows:

$\begin{matrix}0.0235 & 0.0204 & 0.0250 & 0.0218 & {- 0.0582} & {- 0.1054} & {- 0.0098} & 0.0453 & 0.0375 \\0.0221 & 0.0194 & 0.0245 & 0.0130 & {- 0.0577} & {- 0.0936} & {- 0.0058} & 0.0429 & 0.0351 \\0.0268 & 0.0246 & 0.0373 & {- 0.0473} & {- 0.0921} & {- 0.0643} & 0.0221 & 0.0527 & 0.0402 \\0.0295 & 0.0291 & 0.0544 & {- 0.1617} & {- 0.1405} & 0.0143 & 0.0748 & 0.0596 & 0.0404\end{matrix}$

Compared with the unreconstructed displacement matrix I₆, thereconstructed reconstruction matrix I₇ can obtain a smoother and moreconsistent displacement curve, which can in turn obtain a more accurateshear wave velocity V_(s)(t). The method of directly estimating theparticle displacement curve based on the complex matrix constructed fromthe original data and improving the estimation accuracy of velocity bymatrix reconstruction is called first-order estimation.

The above content is a further detailed description of the inventionwith specific preferred embodiments. It cannot be considered that thespecific embodiment of this invention is limited to these descriptions.For those skilled in the art, simple deductions or substitutions whichcan be made without departing from the concept of the invention, shouldbe regarded that it is within the protection scope of the presentinvention.

What is claimed is:
 1. A first-order estimation method of shear wave velocity, comprising the steps of: demodulating entry data, wherein, during an ultrasonic inspection process an ultrasonic echo signal is converted into an electrical signal by an ultrasonic probe, and the electrical signal is converted into digital echo data by an ultrasonic equipment, a data matrix is formed with different echo data obtained at different scanning positions and different scanning times during the ultrasonic inspection process, and the data matrix is formed to an entry matrix I₁ taking IQ data in complex form as data points by a quadrature modulation; calculating a complex angle value, wherein the complex angle value of the complex IQ data of each data point of the matrix I₁ demodulated by the entry data is calculated, and a real number of the corresponding data point is obtained to form an angle value matrix I₂; calculating an average value of the angle value matrix, wherein a real average value of all data at the same scanning position of the angle value matrix I₂ is calculated to obtain a single-column mean value matrix I₃; obtaining an offset matrix, wherein a matching matrix I₄ is introduced, the matching matrix I₄ is a single-row matrix which has the same columns as the angle value matrix I₂ and its data point values are all real numbers “1”, the offset matrix I₅ is obtained by multiplying the mean matrix I₃ and the matching matrix I₄ to obtain; obtaining a displacement matrix, wherein by mutual operations of the angle value matrix I₂ and the offset matrix I₅, the displacement matrix I₆ is obtained which is a displacement value of a particle that changes with time in a propagation of the shear wave; calculating the shear wave velocity, wherein the data of the displacement matrix I₆ is formed into multiple sets of displacement curves on a coordinate axis, and a highest point of each displacement curve is taken to calculate the shear wave velocity V_(s)(t).
 2. The first-order estimation method of shear wave velocity according to claim 1, wherein in the step of demodulation of the entry data, matrix rows of the data matrix are echo information of different scanning positions; and matrix columns are echo information at the same position at different scanning times.
 3. The first-order estimation method of shear wave velocity according to claim 2, wherein in a coordinate system where the displacement curve is located, an ordinate is distance, and an abscissa is time.
 4. The first-order estimation method of shear wave velocity according to claim 2, wherein an expression of the data points of the entry matrix I₁ is Z_(n)=a_(n)+b_(n)*j, and a solution formula of the data points of the angle value matrix I₂ is A_(n) = sin⁻¹(b_(n)/a_(n)).
 5. The first-order estimation method of shear wave velocity according to claim 4, wherein a formula of the shear wave velocity is V_(s)(t) = S_(n)/t_(n), in which s_(n) is a distance difference between the highest point of each displacement curve in each set of displacement curves and t_(n) is a corresponding time difference between the highest point of each displacement curve in each set of displacement curves.
 6. The first-order estimation method of shear wave velocity according to claim 1, wherein the method further comprises the following steps: decomposing and reconstructing the displacement curve, wherein after a singular value decomposition of the displacement matrix I₆, a construction matrix I₇ is obtained based on a singular value matrix obtained by the decomposition.
 7. The first-order estimation method of shear wave velocity according to claim 6, wherein a formula for solving the reconstruction matrix I₇ is I₇=U*S*V, in which U is a left singular matrix, V is a right singularity matrix and S is a diagonal matrix containing singular values. 